The three prime goals of this study are to determine the nature of the alcohol-induced perceptual impairments in the driving situation, to understand the specific psychological processes underlying the changed perception, and to determine how factors such as age, sex, prior drinking history, etc. interact with alcohol in influencing the performance changes. The research focuses on two aspects of driving: (1) the necessity to monitor several sources of information simultaneously (divided attention) and (2) the necessity to rapidly process this data in critical situations. Experimental tools include eye movement and fixation recording of a subject viewing the driving scene, and a series of previously tested measures of concentrated and divided attention, auditory and visual signal detection, rate of information processing, and choice reaction time. The study will utilize these measures, which have been shown sensitive to low alcohol doses and of relevance to complex man-machine performance, to study the above issues and additionally, interaction effects of alcohol and fatigue and potential carryover effects after alcohol metabolization is complete. The studies will attempt to determine the fundamental behavioral mechanisms underlying the sensitivity of divided attention and information processing to alcohol. Finally, the above variables will be examined under the condition of joint consumption of alcohol and marihuana.